An intra-aortic balloon pumping therapy is prescribed for patients who have suffered from deterioration of heart function such as heart failure. Hereinafter, the intra-aortic balloon pumping is referred to as the IABP. More particularly, a balloon catheter is inserted into the patient's aorta such as a descending aorta. A pressurized fluid is introduced or derived from a balloon pump driving system into the balloon catheter in time of the patient's heartbeat. A blood pressure in the patient's aorta can be increased or decreased in response to inflation of a balloon positioned in the aorta or deflation thereof. Therefore, the IABP is an auxiliary circulation apparatus for aiding the deteriorated heart function.
The inflation or deflation of the balloon should be operated relying upon the patient's heartbeat, thereby requiring a speedy response to the patient's heartbeat. In light of foregoing, recent developments have lead to an apparatus in which helium with high response is applied as the pressurized fluid flowing in the balloon catheter, improvements of a balloon pump driving system, and so on.
Japanese Patent Application Publication No. 5 (1993)-16870 discloses one of the above described recent developments. In general, a balloon pump driving system is provided with an isolator divided into an input chamber space and an output chamber space by a movable membrane. The output chamber space communicates with a balloon catheter via a common valve, while the input chamber space communicates with a positive pressure source or a negative pressure source. According to the invention described in the above-described reference, the common valve is closed when the balloon is deflating or while the balloon is under a deflated condition. In this case, the pressure in the output chamber space is increased and maintained at a positive pressure level. The balloon catheter is then set at the positive pressure level at a blast by opening the common valve at a predetermined timing. In the same manner, the common valve is closed when the balloon is inflating or while the balloon is under an inflated condition. In this case, the pressure in the output chamber space is decreased and maintained at a negative pressure level. The balloon catheter is then set at the negative pressure level at a blast by opening the common valve at a predetermined timing.
As described above, a following process can be prepared during a previous process by operatively associating the opening/closing control of the common valve and the pressure control in the output chamber space, thereby enabling to achieve a speedy pressure control.
In the meantime, Japanese Patent Laid-Open Publication No. 10 (1998)-328296 discloses an intra-aortic balloon pump having three isolators; a main isolator, a positive pressure isolator, and a negative pressure isolator. In a process for inflating a balloon, a positive pressure is applied to the balloon by communicating the main isolator and the positive pressure isolator with the balloon. Subsequently, the communication between the positive pressure isolator and the balloon is interrupted, while a predetermined gas is drawn out from the balloon side by the main isolator. Accordingly, an inflation pressure can be assured when the balloon is fully inflated. In the same manner, in a process for deflating the balloon, a negative pressure is applied to the balloon by communicating the main isolator and the negative pressure isolator with the balloon. Subsequently, the communication between the negative pressure isolator and the balloon is interrupted, while a predetermined gas is supplied to the balloon side by the main isolator. Accordingly, a deflation pressure can be assured when the balloon is fully deflated. As described above, in the process for inflating (for deflating) the balloon, a great volume of gas is drawn out of the balloon (is supplied to the balloon) by the main isolator and the positive (negative) pressure isolator. Therefore, a pressure differential can be maintained between the balloon side and the isolator side for a long period of time.
In a conventional system prior to the above-described systems, the pressure differential between the balloon side and the isolator side was decreased with a time-lapse. The balloon inflating speed (the balloon deflating speed) was slowed in response to the decrease of the pressure differential. However, according to the system described in the reference 2, the pressure differential can be maintained until the balloon is fully inflated (deflated). In this case, the pressure differential does not have to be decreased. Therefore, a time required for fully inflating (fully deflating) the balloon can be shortened.